Distillative hydroelectrolysis with alternatively applied pressure



W. F. CURTIS ET AL DISTILLATIVE HYDROELECTROLYSIS WITH Feb. 6, 1968 3,367,848

' ALTERNATIVELY APPLIED PRESSURE 2 Sheets-Sheet 1 Filed Dec. 30, 1965 PIEZOELECTRIC 3 3 ELEMENT llVI/E/VTOH-S WESTLEY E CURTIS HARVEY 4. DAVID o.c. POWER SUPPLY ASYMMETRIC WAVE-FORM GENERATOR ATTYS. 1

Feb. 6, 1968 w. CURTIS ET DISTILLATIVE HYDROELECTROLYSIS WITH ALTERNATIVELY APPLIED PRESSURE 2 Sheets-Sheet 2 Filed Dec. 30, 1965 FIG. 3

FIG. 4.

A TTY-SZ V INVEN TORS WESTLEY E can r/s HARVEY A. DAV/0 United States Patent 3,367,848 DISTILLATIVE HYDROELECTROLYSIS WITH ALTERNATEVELY APPLIED PRESSURE Westley F. Curtis and Harvey A. David, Bethesda, Md,

assignors to the United States of America as represented by the Secretary of the Navy Filed Dec. 30, 1965, Ser. No. 517,861 14 Claims. (Cl. 20349) ABSTRACT OF THE DISCLQSURE An apparatus for evaporating and condensing a liquid, especially water. The apparatus forms vapor bubbles by electrolysing the liquid. The vapor bubbles are subjected to asymmetric wave-form pressure variations, by an electro-acoustic transducer, to produce additional vaporization of the liquid. The vapor is then condensed to a rectified liquid.

The invent-ion described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to evaporating methods and apparatus such as boilers, evaporators and the like, and more particularly to an improved evaporating method and apparatus especially suited, for example, to the product-ion of fresh water from sea water.

The efficient operation of evaporating apparatus such as boilers, fresh water evaporators and the like in which liquid is caused to vaporize in a heat exchanger has been subject to being reduced by the deposition of impurities from the evaporating liquid onto the walls of the heat exchanger, and by the natural tendency of vapor bubbles to form directly on the heat exchanger walls. Both the deposition of impurities and the formation of bubbles reduce the etficient transfer of heat from the exchanger walls to the liquid to be vaporized. The formation of vapor bubbles below the free surface of the liquid is, however, advantageous because of the great increase in area of liquid/vapor interface through which evaporation can take place.

With the foregoing in mind it is one object of this invention to provide improved evaporating method and improved apparatus of the heat exchanger type for carrying out the method wherein the formation of vapor bubbles is encouraged within the body of the liquid and away from the heat exchanger walls whereby the deposi tion of impurities on the walls is minimized and the efiiciency of operation increased.

Another object of this invention is the provision of improved evaporator means for cyclically subjecting the liquid to variations in pressure, for example by electroacoustic transducer, so that during a major portion of each cycle, the liquid experiences an absolute pressure which is less than the vapor pressure, whereby the liquid undergoes rectified evaporation. That is to say, the liquid is caused to vaporize at the liquid/ vapor interfaces of the bubbles at an average rate which is greater than that at which vapor in the bubbles condenses at the interfaces.

Yet another object of this invention is the provision of an improved evaporator apparatus of the foregoing character comprising means for condensing the vapor by bubbling it into the distillate, and wherein the heat given up by the condensing vapor is conducted by the distillate to the heat exchanger walls whereby such heat is recovered for use in forming additional vapor.

ther objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of an evaporator apparatus embodying the present invention;

F IG. 2 is a fragmentary sectional view, on an enlarged scale, of another embodiment of the invention;

FIG. 3 is an enlarged fragmentary sectional view of yet another embodiment of the invention;

FIG. 4 is a transverse sectional view taken along line 44 of FIG. 3; and

FIG. 5 is a fragmentary sectional view taken substantially along line 5-5 of FIG. 3.

In the form of the invention described hereinafter with reference to FIG. 1, there is provided an evaporating apparatus 10 for use in producing fresh water as a distillate from salt water, on board a ship for example. It will be understood of course that the invention may be embodied in evaporators for use with other liquids and for other purposes, the apparatus 10 being exemplary only.

The apparatus 10 comprises heat exchanger means including an outer jacket 11 which is conveniently in the form of a drum having suitable end closures 11a and 11b. A plurality of vertical tubes 12 traverse the interior of the jacket 11 and have their upper ends opening into a common chamber 13 of a vapor collecting header 14.

The tubes 12 are supplied near their lower ends with sea or salt water which enters through openings 15 connected to a make-up water manifold 16 which, for a reason which will presently be made apparent, conveniently enters through the upper region of the jacket end closure 11!) and follows a downward course as at 16a before turning toward the tubes served thereby. The vapor collecting header 14 is provided near the bottom thereof with a brine outlet connection in the form of a pipe 20 which may be connected through suitable valve means to an overboard discharge line.

Within each tube 12, in the lower end portion thereof, is provided an electrode 22 which is supported by a suitable electrically insulated conductor 23 extending through a sealing bushing 24 in the respective tube wall. The electrodes 22 may advantageously terminate in points near the center of each tube and the insulated electrical conductor 23 lead through insulating seals 26 to the exterior of the jacket 11. A source of electrical potential, DC. power supply 135, applied between the conductors 23 and a conductor 27 connected directly to the apparatus It) will effect current flow through the salt water between the electrode points and the walls of tubes 12, thereby electrolysing some of the water and generating minute gas bubbles at the electrode points. The gases generated by electrolysis are principally oxygen, hydrogen and chlorine. The chlorine is almost immediately dissolved in the salt water while the oxygen or hydrogen, depending on the polarity of the applied current source, will emanate as tiny bubbles at the electrode points. These bubbles will, because of their natural bouyancy, rise to ward the tops of the tubes 12 and will enlarge as they rise, due principally to the formation of Water vapor at the gas/liquid interface of each bubble, the rising, enlarging bubbles being indicated at 28 in. the drawings.

The amount of current used need only be that necessary to produce a stream of miniscule bubbles of gas from hydrolized water as the purpose of the electrodes 22 is to provide bubble nuclei for the growth of predominantly water vapor bubbles at a location wholly within the liquid and away from the walls of the tubes 12.

The tubes 12 are closed at their lower ends by plugs or end walls 39 which, in this example are adapted to be flexibly driven by suitable means such as piezoelectric elements 31 which, together with the wall means 30, constitute transducer means, generally indicated as 32. The piezoelectric elements 31 are schematically shown as being provided with suitable electrical connections 33 by which they are energized from a suitable source 35 of electric power, an asymmetric wave-form generator, to cause the wall means 3t) to project compressional wave or sound energy into the columns of sea water contained by the tubes 1.2. The wall means 30 may be suitably configured, for example as shown by the concave surfaces 30a thereof, to direct concentrated or focused beams of sonic or compressional wave energy into the water columns.

The purpose of the transducer means 32, like that of the electrodes 22, is to increase the ability of the apparatus to produce vapor by the addition of energy in a form other than the thermal energy which is supplied through the walls of the tubes 12 to the sea water therein.

To this end, the transducer means 32 is so driven by the power supply 35 as to alternately produce in at least designated portions of the columns of sea water in tubes 12 absolute pressures, which are greater than the vapor pressure within the bubbles 28 and absolute pressures which are less than the vapor pressure within the bubbles, the water being cycled between such pressures so that the pressure is less than the vapor pressure for a major time portion of each cycle. That is to say, the time period of each cycle during which the pressure of the water is less than the vapor pressure exceeds the time period of each cycle during which the pressure of the water is less than the vapor pressure exceeds the time period of each cycle during which the pressure of the water is higher than the vapor pressure. Note that, by controlling the wave-form of the input to the transducer, the foregoing cycling can be done without attempting to change the average pressure in the vicinity of the bubble. It is recognized that any attempt to change the average pressure at a point in the interior of a liquid will result in motions of the water which will at least make it very difficult if not completely impractical to produce an appreciable change in the average pressure by supplying some energy. However, if in the positive position of the sound-pressure cycle, the increase in pressure is made relatively large and of a relatively short duration, the decrease in pressure during the negative portion of the sound pressure could be relatively small, thus making its duration relatively long without requiring a change in the average pressure. The rate of recondensation will depend primarily on the surface area of the bubble and the density of the vapor, which in turn depends on the pressure within the vapor.

As the density of the liquid is much higher than the density of the vapor (for water the ratio is of the order of 1000:1) much of the sound pressure applied to liquid is used up in accelerating the water near the surface of the bubble; furthermore it requires time to move this water. It follows that the vapor is not compressed as much as might be expected and the rate of recondensation is consequently not as high. The rate of evaporation will depend briefly upon the temperature of the liquid at the surface of the bubble; this will be almost entirely controlled by the necessity of balancing the heat loss due to evaporation against the heat gained by conduction and convention from the body of the liquid; the pressures and velocities due to the sound energy will have little influence. On the basis of a qualitative type of argument then the conclusion is reached that there will be rectified evaporation which will favor evaporation analogously to the way in which rectified difiusion is known to favor the extraction of dissolved gases from liquids. Furthermore, it appears that rectified evaporation will be more effective if the sound frequency is rather high (thus making the duration of a cycle short) and if the waveform is asymmetric so that the pressure is decreased throughout the greater part of the pressure cycle.

During those portions of the cycles when the water columns in tubes 12 are subjected to absolute pressures greater than the vapor pressure of the bubbles therein, vapor tends to condense in the bubble and to reduce the size of the bubble. However, during the longer portions or time periods of the cycles during which the absolute pressure of the water columns is less than the vapor pressure of the bubbles therein, Water vaporizes at the vapor/liquid interfaces of the bubbles and contributes to increase in size of the bubbles and total quantity of water vapor. The net result of the alternating, but unequal duration, of the pressures is to produce rectified evaporation of water into the vapor state in the bubbles. Thus, the introduction of sound or compressional wave energy in the manner just described enhances the production of water vapor under the influence of thermal energy supplied through the walls of tubes 12 acting as a heat exchanger in the otherwise usual manner. From the above it will be apparent that the term compressional wave as used herein contemplates the existence of rarefactions between higher pressure zones, and that the rarefactions are of greater duration than the higher pressure zones at a given point in the liquid.

The rising water vapor is collected in the vapor collecting header 14 from which is withdrawn through a vapor outlet pipe 40. The withdrawn vapor is then condensed in any well known manner to provide useable fresh Water. In the present example the heat given up by the condensing vapor is advantageously utilized to contribute to the heat required in the vaporizing of the sea water within the tubes 12.

For that purpose the apparatus 10 comprises a suitable pump 42 having its intake connected to the vapor outlet pipe 46 from the vapor collecting header 14. The pump 42, which may be driven by an electric motor or the like, has its outlet connected to a pipe 44 which extends downwardly into the heat exchanger jacket 11 and then runs adjacent the lower end portions of the tubes 12. The pipe 44 is provided with a series of openings 45 from which the vapor escapes into the heat exchanger jacket 11 surrounding the tubes 12. The jacket 11 is filled with fresh water condensate which is maintained at a pressure greater than the vapor pressure within the tubes 12 so that the vapor escaping as bubbles 46 will condense into the condensate as they rise along the outer surfaces of the tubes 12, thereby giving up thermal energy to the condensate surrounding those tubes. This thermal energy is passed through the walls of tubes 12 to the sea water therein and contributes to the formation of additional vapor.

The pressure within the jacket 11 may conveniently be maintained by means of a stand-pipe 48 and surge tank 49. The latter is provided with a suitable outlet and valve 50 at the upper region thereof through which such excess vapor may be withdrawn as finds its way to the surge tank. Of course the pressure provided in pipe 44 by the pump 42 must exceed the pressure provided in the jacket 11 by the stand-pipe 48 and surge tank 49 so as to insure a flow of vapor into the condensate. The jacket 11 is provided with a pipe 51 and valve 52 through which the condensate can be withdrawn from the jacket at a rate substantially equal to the rate at which it is formed by the condensing vapor bubbles 46.

A baflle 55 is conveniently placed within the jacket 11 and around which a circulation of distillate will be set up in the direction of the arrows 56 by the Warming effect of condensing vapor bubbles 46 to the left of the bafiie as illustrated. The portion 16a of the sea water inlet manifold 16 will thereby be subjected to a warming current of Water so that the incoming sea water will be warmed somewhat prior to introduction to the tubes 12 via the openings 15.

The distillate in the heat exchanger jacket 11 may be further heated to promote vaporizing within the tubes 12 by the use of waste heat from engine exhausts or the like as is commonly done in the operation of low temperature evaporators. This may be conveniently accomplished through the use of heat exchanger tubing 57 through which hot exhaust gases, engine water jacket coolant, or the like may be passed.

A plurality of similar evaporator apparatuses may be connected in series and operated at successively reduced temperatures to gain overall efliciency. In this arrangement the vapor output from the pump 42 of the first, highest temperature evaporator would be connected to the conduit 44 of the second, next lower temperature evaporator so that vapor from the first would be condensed in the jacket 11 of the second. The vapor from the pump 42 of the second could be condensed in the jacket 11 of the third still lower temperature evaporator, and so on, the vapor from the last evaporator being condensed in its own jacket or in any other suitable condenser of known construction.

The piezoelectric elements 31 forming part of the transducer means 32 of the afore-described apparatus 10 may comprise suitable crystal or ceramic elements which are consistent with the operating temperatures of the apparatus, usually relatively low in the case of fresh water evaporators. When the invention is practiced at higher temperatures, however, such as in the case of steam boilers or the like, the transducer means 32 may advantageously be of electromagnetic, magnetostrictive, or like construction which is more compatible with higher temperatures.

One alternative transducer construction is illustrated in FIG. 2 wherein parts corresponding to parts of FIG. 1 are given cooresponding reference numerals with prime marks added. In this embodiment a boiler or evaporator tube 12 has its lower end passing through the heat exchanger jacket 11 and is closed by a sound energy transmitting bar 60 having its upper end portion fixed in the tube 12' by a somewhat flexible sealing ring 62 of metal or suitable cement. The bar 60 extends for the greater portion of its length below the ring 62.

A piezoelectric element 31' is supported against the lower end of the bar 60 by a support member 63 which depends from the jacket 11' and includes an opening 63a for electrical conductor means 33' leading from the piezoelectric element. The sound transmitting bar is preferably formed of a material such as glass which has good sound wave transmitting properties, is heat resistant, and can provide reasonable thermal insulation for the piezoelectric element which may be cemented directly to the rod. The upper side of the piezoelectric element may, if necessary be metal plated, as shown at 64, to provide for electrical connection of a conductor 65 thereto.

The length of the bar 60 should be sufiicient to provide the necessary thermal insulation, and desirably the frequency of the sound should be chosen so that the wave length of the compressional wave in the rod is less than twice the diameter of the rod so as to prevent high attenuation in the rod. Moreover, this will assure that the wave length of the sound in the liquid in the tube is less than the diameter of the radiating face 60a of the bar, which may be suitably configured to project a beam of sound energy. Additionally the position of the sealing ring 62 along the length of the rod 60 should be chosen so that at the desired frequency a standing wave system will be set up which will have a node at the sealing ring and a loop at the upper end of the rod.

Again, the piezoelectric element 31' may be replaced by other means such as magnetostrictive means for driving the rod to produce the previously described sound or compressional wave characteristics necessary to subject the liquid column in the tube 12' to alternating pressures greater and less than the vapor pressure of the liquid, whereby the rectified diffusion of liquid to vapor takes place.

Because bubbly liquids attenuate sound very readily, it would be desirable in the instance of relatively long tubes 12 or 12' to utilize a plurality of transducers spaced along the lengths of the tubes. If the working temperatures are not too high, the transducers may be disposed within the liquid at intervals along the tubes, and the electrical inputs thereto phased as though the transducers within each tube were an end-fire transmitting array, thereby tending to concentrate the sound energy within the tubes.

If there is difficulty in insonifying the upper portions of the boiler tubes, and if the working temperature is too high to permit placing transducer active elements within the tubes, the embodiment described hereinafter with references to FIGS. 3-5 may be used to advantage. In those figures, parts corresponding to parts in the embodiments of FIGS. 1 and 2 are given corresponding reference numerals but with double prime marks. Thus, a boiler tube 12 has its lower end extending through the heat exchanger jacket 11" and is provided with electro-acoustic transducer means generally designated 32". The end portion of the tube 12" is closed off by a resiliently flexible diaphragm or wall 70 through which extends a long, narrow flexible glass or metal strip 71, the strip being generally centrally aligned within the tube and being welded or otherwise sealingly fixed to the wall 70 through which it passes. The portion of the strip 71 extending below the wall 70 passes between two bender type piezoelectric elements 73, 74 which are supported as by being cemented between the strip and support members 76 and 77, respectively, depending from the jacket 11". The piezoelectric elements 73, 74 are provided with suitable electrical connections 78, 79 and 78a, 79a for energization by electrical inputs suitably phased so that element 73 contracts when element 74 expands, and vice-versa. Such energization is utilized preferably to excite the strip 71 into flexural vibrations as is shown by dot and dash lines in FIGS. 3 and 4, it being understood that the displacements so representated are greatly exaggerated for purposes of clarity. A standing wave system with wave length much smaller than the length of the strip 71 is desirably set up by choosing appropriate strip dimensions, materials and operating frequency, the standing wave being characterized by a node at the wall 70 and a loop at the upper end of the strip. For purposes of running the strip 71 for maximum response, an adjustable mass 80 is conveniently supported on the terminal end of the strip 70 by a nut 81 threadedly engaged on a stem 82 at the lower end of the strip.

A pair of vertical vanes 85 are preferably fixed Within the tube 12" and are substantially coplanar with the strip 71 when the latter is at rest. The vanes 85 cooperate with the flexing strip 71 to produce the desired pressure changes in the liquid in the boiler tube 12", those pressure changes being as described heretofore. That is to say, to produce absolute pressures alternatively greater and lesser than the vapor pressure concerned, the lesser pressures being for the major time portion of the cycles of alternation.

It will be understood that although the apparatus described shows both usedsimultaneously, the invention also contemplates the use of either the electrode means or the transducer means independently of the other as means for adding energy to an evaporator system to improve the production of vapor for a given thermal input.

From the foregoing detailed description of several exemplary embodiments of the invention, it will be appreciated that the previously stated objects and advantages, as well as others apparent from the description, have been attained by the invention.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

7 What is claimed is: 1. A method of evaporating liquid, said method comprising the steps of:

providing a column of liquid to be evaporated; forming bubbles in said liquid by electrolysis; and cyclically subjecting said liquid to alternating pressures greater and lesser than the vapor pressure of said liquid, the liquid being subjected to the lesser pressures for a major time portion of each cycle whereby liquid is encouraged to vaporize into said bubbles at a greater rate than liquid condenses therefrom. 2. The method of evaporating liquid as defined in claim 1 and wherein said alternating pressures are characterized as compressional waves.

3. Evaporator apparatus comprising: heat exchanger means including wall means for confining an essentially vertical column of a liquid to be vaporized and jacket means for confining a heating medium against said wall means for supplying thermal energy therethrough to eiTect vaporization of said liquid; means for collecting vapors of said liquid; transducer means operable to transmit compressional waves into said liquid; and power supply means for driving said transducer means to alternately subject at least zones of said liquid to pressures less than the vapor pressure thereof and to pressures greater than the vapor pressure thereof, the liquid being cycled between such pressures with the pressures less than the vapor pressure of the liquid being for the major time portion of each cycle. 4.. Apparatus as defined in claim 3 and further comprising:

pump and conduit means connected to said means for collecting said vapor, and operative to discharge said vapor into distillate in said jacket, whereby vapor condenses in said distillate and gives up thermal energy for transfer by said wall means to said liquid being vaporized. 5. Apparatus as defined in claim 3 and further comprising:

means for generating bubbles in said liquid as nuclei for growth of predominantly vapor bubbles. 6. Apparatus as defined in claim 5 and wherein said means for generating bubbles comprises:

electrode means disposed in said liquid column in the lower portion thereof; and

means for applying electrical potential to said electrode means.

7. Apparatus as defined in claim 3 and wherein:

said transducer means comprises electro-acoustic transducer means for vibrating a confining wall means of said vertical column.

8. Apparatus as defined in claim 3 and wherein:

said wall means comprise a vertical boiler tube; and

said transducer means comprises a rod of compressional wave transmitting material having an upper end portion extending into the lower end of said tube and retained therein by sealing means, a lower end portion extending below said sealing means, a piezoelectric element disposed against the lower end of said rod and thermally insulated by said rod from said liquid, and support means depending from said jacket and supporting said piezoelectric element against said rod.

9. Apparatus as defined in claim 3 and wherein:

said wall means comprise a vertical boiler tube;

said transducer means comprises resilient sealing means for the lower end of said tube, an elongated flexible strip having an upper portion extending upwardly into said tube above said sealing means, said strip extending through and below said sealing means, piezoelectric means engaging the lower portion of said strip and operable by said power supply means to cause said strip to undergo fiexura'l vibrations within liquid in said tube.

10. Apparatus as defined in claim 9 and comprising:

mass means supported by the lower end portion of said strip, said mass means being adjustably positionable along said lower end portion of said strip to selectively tune the strip for maximum response at a predetermined frequency of vibration.

11. Apparatus as defined in claim 6 and wherein:

said transducer means comprises electro-acoustic transducer means for vibrating a confining wall means of said vertical column.

12. Apparatus as defined in claim 11 and wherein:

said wall means comprise a vertical boiler tube; and

said transducer means comprises a rod of compressional wave transmitting material having an upper end portion extending into the lower end of said tube and retained therein by sealing means, a lower end portion extending below said sealing means, a piezoelectric element disposed against the lower end of said rod and thermally insulated by said rod from said liquid, and support means depending from said jacket and supporting said piezoelectric element against said rod.

13. Apparatus as defined in claim 6 and wherein:

said wall means comprise a vertical boiler tube;

said transducer means comprises resilient sealing means for the lower end of said tube, an elongated flexible strip having an upper portion extending upwardly into said tube above said sealing means, said strip extending through and below said sealing means, piezoelectric means engaging the lower portion of said strip and operable by said power supply means to cause said strip to undergo flexural vibrations within the liquid in said tube.

14. Apparatus as defined in claim 13 and comprising:

mass means supported by the lower end portion of said strip, said mass means being adjustably positionable along said lower end portion of said strip to selectively tune the strip for maximum response at a predetermined frequency of vibration.

References Cited UNITED STATES PATENTS 2,265,762 12/ 1941 McKittrick et al 20339 2,417,722 3/1947 Wolff 204-157 X 2,449,587 9/ 1948 Chambers 203-99 X 2,717,874 9/1955 Verain.

2,891,176 6/1959 Branson 683 X 2,928,778 3/1960 Heathfield et al. 204149 3,000,795 9/ 1961 Goeldner 203-24 X OTHER REFERENCES Alfred Weissler, Journal of the Acoustical Society of America, Vol. 25, No. 4, July 1953, pp. 651 to 657.

NORMAN YUDKOFF, Primary Examiner.

WILBUR L. BASCOMB, JR., Examiner.

D. E. EDWARDS, Assistant Examiner. 

